Field of the Invention
The present disclosure relates to photoconductors, image forming apparatuses including the photoconductors, and process cartridges including the photoconductors.
Description of the Related Art
In an image forming method using an image forming apparatus, an image is formed by subjecting a photoconductor to, for example, a charging step, an exposure step, a developing step, and a transfer step. Recently, an organic photoconductor containing an organic material is widely used as a photoconductor because of advantages such as flexibility, thermal stability, and film-forming property.
Recently, there is a need for photoconductors to have greater degrees of durability and stability along with rapid advancement in full-color, high-speed, and high-definition properties of image forming apparatuses. Moreover, improvement in a surface layer such as a protective layer drastically improves the photoconductor in wear durability. Meanwhile, there is a need for each layer constituting the photoconductor (e.g., a photoconductive layer, an intermediate layer, and an undercoat layer) to have electric durability, chemical durability, and stability of electric property to fluctuation of usage environment.
An organic material constituting a photoconductor gradually changes in quality through electrostatic load in the typical electrographic process including repetitive charging and charge eliminating. As a result, the photoconductor is deteriorated in electric property, and cannot retain electric stability when the photoconductor is used for a long term. It is known that deterioration in charging property considerably adversely affects quality in output images, and causes serious problems such as deterioration in image quality, background fog (hereinafter may be referred to as background stain, fog, and black spots), poor uniformity of images during continuous outputs. It is believed that these problems are closely related to the undercoat layer of the photoconductor. Therefore, improvement in the undercoat layer is necessary in order to obtain durability and high stability of the photoconductor.
Generally, an organic photoconductor includes a conductive support containing, for example, aluminium, an undercoat layer disposed on the support, and a photoconductive layer disposed on the undercoat layer. The undercoat layer is a conductive layer mainly containing a binder resin and conductive particles such as metal oxide particles, and is disposed in order to achieve three objects: “function of leak resistance”, which is obtained by covering the surface of the support with the undercoat layer; “function of preventing injection of charges” from the support to the photoconductive layer; and “function of transporting charges” to the support, where the charges are generated in the photoconductive layer. The undercoat layer is required to improve these functions.
As the typical undercoat layers, proposed is an undercoat layer containing titanium oxide particles (see Japanese Unexamined Patent Application Publication No. 2003-98705). Moreover, proposed is a method for imparting leak resistance to an undercoat layer by disposing an intermediate layer on the undercoat layer (see Japanese Unexamined Patent Application Publication No. 2007-047467).
Additionally, another proposed undercoat layer has a film thickness of 10 μm or less, and contains titanium oxide particles, and zinc oxide particles that are subjected to hydrophobic treatment with a reactive organic silicon compound (see Japanese Unexamined Patent Application Publication No. 2008-299020). Meanwhile, another proposed undercoat layer contains tin oxide particles or zinc oxide particle (see Japanese Unexamined Patent Application Publication No. 2003-084472). Another undercoat layer contains salicylic acid or a thiol-group-containing compound (see Japanese Unexamined Patent Application Publication No. 2008-96527).
Meanwhile, another proposed undercoat layer contains conductive metal oxide particles (zinc oxide particles) that are surface-treated with the silane coupling agent (aminosilane), and when a film thickness of the undercoat layer is 20 μm, transmittance of the undercoat layer to light having 950 nm is 85% or more, and volume resistivity of the undercoat layer is 1×1010 Ω·cm or more but 1×1012 Ω·cm or less (see Japanese Unexamined Patent Application Publication No. 2007-322996).
None of the above documents of the related art has provided a photoconductor containing an undercoat layer, and having stable electric property even if used for a long term, and being can be prevented from causing an afterimage during image formation and background fog, where the undercoat layer satisfies all of the following functions necessary for the undercoat layer to have: the function of leak resistance, the function of preventing injection of charges, and the function of transporting charges.